1. Field of the Invention
The present invention pertains generally to integrated circuit fabrication on silicon starting material.
2. Description of the Background
Typical bipolar and BiCMOS integrated circuits are manufactured on p-type silicon substrate wafers. The substrate of these wafers is used as the starting material for the integrated circuit fabrication. Generally, early in the process an epitaxial silicon layer is grown on the starting material. It is in this epitaxial layer that the semiconductor devices such as transistors, diodes, resistors, capacitors or other devices are fabricated.
Typically, before the epitaxial layer is grown, a buried layer is fabricated at the interface of the epitaxial layer and the silicon starting material in order to reduce series resistance within the device.
The quality and yield of the integrated circuit depends upon many factors. One of these factors is the quality of the epitaxial layer. This layer needs to be as uniform and consistent in its crystal orientation and structure as possible. Defects or deformities in this crystalline structure cause electrical problems and specifically, collector to emitter shorts among other problems.
In the standard process, because the wafer substrate is used as the starting material, interstitial oxygen in the starting material precipitates during thermal cycles. These precipitates nucleate stacking faults. The stacking faults are used to absorb metal contaminants which can cause electrical problems.
However, these stacking faults can also intersect the surface of the starting material. When this occurs, the stacking faults are replicated in the epitaxial layer grown on top of the starting material causing deformities in the crystalline structure, that in turn cause electrical problems.
Prior art solutions addressed this problem by depleting the substrate surface of oxygen before growing the epitaxial layer by backing the substrates in a diffusion furnace in a process known as denuding. This procedure, however, does not completely deplete the substrate surface of oxygen, it only reduces the amount of oxygen at the substrate surface. Since this procedure still leaves some oxygen, the remaining oxygen precipitates at the substrate surface and nucleates stacking faults. There remains a need to virtually eliminate the oxygen and thus the stacking faults.